5 - Physiology of tooth movement and appliances overview Flashcards
What are the different types of tooth movement?
- physiological (mesial drift and tooth eruption)
- orthodontic (externally generated forces)
Described the physiological basis of orthodontic tooth movement.
- external force applied to tooth
- bony remodelling occurs around the tooth to facilitate movement
- movement is dictated by PDLs
Describe the differential pressure theory.
In areas of compression the bone is resorbed and in areas of tension, bone is deposited.
What are the different theories of orthodontic tooth movement?
- piezo-electric theory (historic)
- differential pressure theory
- mechano-chemical theory
What are the types of orthodontic appliance?
- removables
- functionals
- fixed
What are the different types of orthodontic tooth movement?
- tipping
- bodily
- intrusion
- extrusion
- rotation
- torque (move root instead of crown)
How much force is required to produce a tipping movement?
35-60 grams
How do functional appliances work?
- mandible is postured away from normal position
- facial muscles are stretched which generates forces that are transmitted to teeth and alveolus
- restrict maxillary growth but promote mandibular growth and remodel the glenoid fossa
- uppers become more retroclined and lowers become more proclined
How much force is required to produce bodily movement?
150-200 grams
How much force is required to produce an intrusion movement?
10-20 grams
How much force is required to produce an extrusion movement?
35-60 grams
How much force is required to produce a rotational movement?
35-60 grams
How much force is required to produce a torque movement?
50-100 grams
Describe the histological changes brought about by light orthodontic force.
- hyperaemia within the PDL
- appearance of osteoclasts and osteoblasts
- resorption of lamina dura from pressure side (clasts)
- deposition of osteoid on tension side (blasts)
- frontal remodelling of socket
- PDL reorganises
- gingival fibres remain distorted
Why is relapse common after light orthodontic forces?
The gingival fibres do not reorganise and remain distorted which can move tooth back to original position
Describe the histological changes brought about by moderate orthodontic forces.
- occlusion of vessels of PDL on pressure side
- hyperaemia of vessels of PDL on tension side
- hylinisation on pressure side
- period of stasis 10-14 days
- increased endosteal vascularity (ie undermining resorption)
- sudden movement of tooth (can feel loose)
- PDL heals and remodels
Describe the histological changes brought about by excessive orthodontic forces.
- extensive lateral root resorption and undermining resorption
- PDL necrosis
What are the side effects of excessive orthodontic force?
- pain
- necrosis and undermining resorption
- anchorage loss
- possible loss of tooth vitality
What factors affect the response to orthodontic force?
- magnitude
- duration
- age
- anatomy
What is the threshold of duration of wear required to see some tooth movement?
6 hours/day
How does age affect tooth movement?
Movement occurs more quickly in younger patients
What is alveolar necking?
- thinner bone where a tooth has been lost
- thick cortical plates
- difficult to move tooth through
Does RCT prevent orthodontic treatment?
Can be orthodontically treated if there is no associated pathology and the PDL is intact
